Hepatic microsomal monooxygenases (P-450) of untreated rats will be isolated and subfractionated into their component species to determine how many different P-450 species exist and their characteristics. The role of the membrane in the monooxygenase function will be studied by determining the effect of lipid on the temperature sensitive spin state transition. The necessity for lipid will be assessed on total P-450 of the membrane and purified individual P-450 types, to ascertain by different metabolites formed from the same substrate whether control by lipid is exerted on the different P-450's. The hypothesis that the lipid controls spin state equilibrium response to substrate, that the equilibrium affects oxidation-reduction potential and that this modulates activity will be assessed.